Another thing she told me was that she would like to stay an extra 30 days after the closing date, meaning that she would like to move out on the 28th of July.

Then we want to buy another duplex with the same price and a 5% down payment under my mom's name since she will be living in 1 unit and rent the other unit out.

I am now approaching 115+ days since assignment on my first 3 deals and because I am in NYS, my attorney tells me that I cannot even speak to buyer’s or seller’s attorneys due to “breach of contract”.I lost my first deal in fact because we were hindering on 130 days since assignment (should have been long closed) and the city decided to demo before we closed and were able to takeover in court. 

I’m new to the real estate field & just recently worked with an out of state client who was going down the same route!

I posted a 60 day notice to terminate the lease (the lease says 60...), the same day I receive a message from her boyfriend (I think) who I met once briefly but does not live at the property, saying that she is not living there, and that she cant be reached.

The exact settings depend on your strategy.For example, you can set the next 14 days with a minimum stay of 2 nights for STR bookings.

Same thing in Spain.

When evaluating MTR markets I would always start by searching Furnished Finder and Airbnb/VRBO (30+ day stays) to get a good sense of what is out there on the market already.

Regardless they all act the same.  

@Jackie Linne It may be worthless if the earn a "high salary" in their day jobs too...